The present invention relates to a pneumatic tire provided in the tread portion with shoulder blocks capable of improving wandering performance.
In pneumatic tires provided in the tread portion with a rigid belt, such as heavy duty tires for trucks and buses, the rigidity of tread shoulder portions is increased by the belt, and a wondering phenomena tends to occur when running on irregular road surfaces such as rutted road surface.
Hitherto, therefore, in order to improve the wondering performance of a tire, the following means are widely employed: disposing a circumferentially extending narrow groove (a) near each tread edge TE as shown in FIG. 4; disposing axially extending sipes or cuts in each tread edge TE as shown in FIG. 5; and providing tire shoulders (b1) with a round contour as shown in FIG. 6.
The narrow grooves (a) and sipes inevitably decrease the rigidity of the tread edge portions. Therefore, uneven wear is liable to occur. Also, tear-off of tread rubber is liable to occur. In case of the round shoulders (b1), as the ground contacting width decreases and the tread edges are devoid of edged corners, it is difficult to improve running performance such as grip performance during straight running and cornering and the like.
It is therefore, an object of the present invention to provide a pneumatic tire in which the wandering performance can be effectively improved without causing uneven wear, rubber tear-off, deterioration in running performance and the like.
According to the present invention, the pneumatic tire comprises a tread portion provided along each tread edge with a circumferential row of shoulder blocks, each shoulder block having an axially outer side face which is convexly curved in a plane parallel to the tread surface. The convexly curved axially outer side face extends radially inwardly from the top of the shoulder block to a radial distance which is not less than 60% of the height of the shoulder block.